In mobile phones, smart phones, touch panels and other devices, which are equipped with an image display section, the image display section have conventionally employed the following structure (an air gap structure). That is, an air gap is made between an image display unit, such as a liquid crystal display module, and a transparent cover plate put on top of the image display unit (e.g., a glass plate, a tempered-glass plate, an acrylic board, a PET or polyethylene terephthalate board, and a composite substrate including any of them). Such a structure avoids separation of the cover plate from the image display unit, which can be occurs because of separation force applied to the cover plate due to external stress, and avoids display defects due to external force being applied to the display unit.
In recent years, for the purpose of improving visibility and adhesion of the display unit, a part of such devices employs a structure that a cover plate and the display unit is adhered with optical elasticity resin which can be cured by light. In apparatuses which are desired to have enhanced design characteristics and enhanced decoration characteristics of the display unit (e.g., a car navigation system and a tablet terminal), a cover plate decorated by printing is used, and the screen size for those apparatuses tends to become larger.
FIG. 24 illustrates a conventional display apparatus disclosed in International Patent Application Publication WO2007/066590 (corresponding to US2009/162645A1). The conventional display apparatus includes: a transparent cover plate 21; a light-shielding printed member 22 prepared by printing with black ink and arranged on the rear surface of the transparent cover plate 21 around the periphery of a display area of the transparent cover plate 21;a display unit including a TFT (Thin Film Transistor) substrate 23, a CF (Color Filter) substrate 24, a phase difference correction film 25, a polarization plate/optical film 26, and a driver IC 27; and a transparent photo-curable resin 28 that bonds the transparent cover plate 21 and the entire surface of the display unit together.
The thickness of the photo-curable resin 28 is in the range of 30 μm to 200 μm and the protrusion of the photo-curable resin 28 from the outer periphery of the display unit is within about 0.3 mm. The part sandwiched by the light-shielding printed member 22 and the display unit is not irradiated with light coming from upward of the cover plate or downward of the display unit. Therefore, light is irradiated from a lateral direction of the outer circumference of the cover plate so as to cure the photo-curable resin 28 to have the curing degree of 70% or more.
FIG. 25 illustrates a structure of a conventional display apparatus disclosed in Japanese Unexamined Patent Application Publication (JP-A) No. 2013-088455. The conventional display apparatus includes: a transparent cover plate 31; a light-shielding printed member 32 prepared by printing with black ink and arranged on the rear surface of the transparent cover plate 31 around the periphery of a display area of the transparent cover plate 31; a display unit including a flat panel display unit 33, a backlight 34 and a bezel 35; a dam section arranged on an outer-edge area of the transparent cover plate 31; and a transparent photo-curable resin 37 that adheres the transparent cover plate 31 and the entire surface of the display unit together.
The dam section 36 is formed by applying photo-curable material onto the transparent cover plate 31 in advance to form a bead shape having height of 150 μm and width of 1 mm and then curing the photo-curable material by light. A predetermined amount of photo-curable resin 37 is applied on the inner side of the dam section 36 so as to have the thickness of 150 μm, the transparent cover plate 31 is joined together with the display unit, and the photo-curable resin 37 is fully cured by irradiation of UV light or the like.
In WO2007/066590, the photo-curable resin 28 on a location sandwiched by the light-shielding printed member 22 on the transparent cover plate 21 and the display unit has a uniform curing degree not less than 70%. In addition, in JP-A No. 2013-088455, the photo-curable resin 37 has a uniform curing degree and is fully cured.
In WO2007/066590 and JP-A No. 2013-088455, photo-curable resin on a location sandwiched by the transparent cover plate and the display unit is cured to have a uniform high curing degree. Accordingly, when the transparent cover plate is deformed by external force, such a deformation makes the stress applied to the display area to cause display defect. In addition, under the condition that the photo-curable resin is cured with a uniform curing degree to have a low curing degree, such a condition can make a problem that external force can separate the transparent cover plate from the display unit.
In addition, the dam section 36 is provided to avoid the photo-curable resin 37 from flowing outside the display unit and therefore the resin does not reach to the end of the display unit in JP-A No. 2013-088455. Thus, there are issues of the transparent cover plate 31 is easily separated from the display unit as a result of external force from the end of the transparent cover plate 31. Such a condition can make a problem that external force applied from the end of the transparent cover plate 31 can easily remove the transparent cover plate from the display unit.
The present invention seeks to solve the problems.